Apparatus and method for determining objective refraction using wavefront sensing

ABSTRACT

An apparatus for determining the objective refraction of a patient&#39;s eye includes a transparent window and a wavefront measurement device that determines aberrations in a return beam from the patient&#39;s eye after the beam passes through a corrective test lens in the apparatus. The wavefront measurement device outputs an instant display representative of the quality of vision afforded the patient through the test lens. The display can be a representation of a Snellen chart, convoluted with the optical characteristics of the patient&#39;s vision, an overall quality of vision scale or the optical contrast function, all based on the wavefront measurements of the patient&#39;s eye. The examiner may use the display information to conduct a refraction examination and other vision tests without the subjective response from the patient.

FIELD OF THE INVENTION

The present invention relates generally to methods and apparatus fordetermining a person's visual characteristics, and more particularly toapparatus for determining the refraction of the eye.

BACKGROUND

Phoropters are apparatus used by optometrists to determine a patient'svisual characteristics, so that proper eye diagnoses can be made andeyewear can be prescribed. In conventional phoropters, a patient looksthrough the phoropter, in which various test lenses are disposed, at atarget eye chart, referred to as a “Snellen chart”, while an optometristmoves the test corrective lenses into the patient's field of view. Insome applications, the target may be positioned at a predetermineddistance from the patient. The patient is then asked to verbally comparethe quality of the perceived image as afforded by one lens versus theprior lens presented. The optometrist takes note of either animprovement or a deterioration in the patient's vision through suchlenses. Systematically, the test progresses towards the “best” test lensentirely based on the patient's responses. The lens parameters are thenused as the basis for a prescription for eyewear.

Unfortunately, as recognized herein the patient can become fatiguedduring the process and/or misjudge the vision afforded by the variouslenses. This can lead to the selection of a less than optimumprescription. Moreover, some patients, such as a very ill or a veryyoung patient, might not be capable of articulating the quality ofvision the various lenses afford the patient.

Objective methods of determining the patient's refraction errors havebeen proposed, but these other methods introduce further complicationsthat are not present when using phoropters. In a retinoscopy method, forexample, a streak of light is projected to a patient's retina, and thecharacteristics of the reflected light at the patient's corneal plane isanalyzed to determine whether the patient is myopic, or hyperopic, andwith or without astigmatism. However, the method does not providesufficient accuracy for prescribing spectacle lenses. Consequently, itsmeasurement results are typically used only as a starting point of astandard phoropter measurement.

Another objective measurement instrument for determining refractiveerrors is an autorefractor, which, owing to its speed of use, is morepopular than retinoscopy. To use the autorefractor, a patient is askedto look inside an enclosed box that is part of the autorefractor. Atarget image is optically projected into patient's eye, and a series oflenses is automatically moved into position of the patient's line ofsight to the target, to neutralize the patient's refractive errors(autorefraction). Unfortunately, the measurement outcome often differsfrom the patient's ideal prescription. Accordingly, like retinoscopy,autorefractor outcomes typically are used only as starting points forstandard phoropter measurements.

Moreover, both retinoscopy and autorefraction fail to account for theaccommodation effect of the patient, that is, for the propensity of apatient to alter his or her focus or sight to make the best of thevision test. An autorefractor measurement essentially is a snapshot ofthe patient's vision at a particular instant at which the autorefractorhas identified a so-called neutralization point, and at this point if ithappens that the patient focuses his vision for seeing an image at adistance other than what is intended, or if the patient is momentarilylooking elsewhere other than the target, the output of the autorefractoris erroneous. Such deceptive focussing on the part of the patient canarise because the patient is conscious of the working distance insidethe box, and when an image of an object presented to the patient whichis modelled to be located at, e.g., twenty feet, the patientautomatically focusses for an image at a much closer distance, knowingthe actual size of the box. Examination results that include patientaccommodation effects are inaccurate for prescribing spectacle lenses.

Another limitation of the autorefractor is that the examiner has nocontrol over which lens is to be used in test. The result is thatrepeated measurements are likely to provide different results for thesame eye from the same patient, which results in laborious and timeconsuming tests and retests when using the device to finalize aprescription. The present invention, having made the above-notedcritical observations, provides the solutions disclosed herein.

SUMMARY OF THE INVENTION

A phoropter includes plural test lenses that can be disposed into a lineof sight defined between a patient and a target, such that a patientlooking at the target perceives light from the lens. A wavefrontmeasurement apparatus is positioned to detect aberrations in lightreturning from the patient. The aberrations are caused by the eye of thepatient.

In a preferred embodiment, the wavefront measurement apparatus includesa light source, such as a laser, for generating the light and a lightdetector that outputs a signal representative of the aberrations. Also,the apparatus includes a processor that receives the signal from thelight detector and outputs a diagnostic signal representative thereof.The diagnostic signal is useful for generating an image representativeof the test object, and/or for generating at least one visual displayrepresentative of an effectiveness of the lens in correcting a patient'svision. The visual display can include a bar chart, a pie chart, and/ora line chart, and it can be color coded.

In another aspect, a method for indicating the quality of a patient'svision includes providing a device through which a patient can look at atarget. The method also includes directing a laser beam into the eye ofa patient when the patient looks at the target, and then detectingaberrations in a wavefront of the light beam as the light beam returnsfrom the patient's eye. Based on the wavefront, the method indicates aquality of a patient's vision.

In still another aspect, a method for indicating the quality of apatient's vision includes providing a device into which a patient canlook, and that generates an instantaneous visual indication of a qualityof a patient's vision.

In yet another aspect, a device for aiding a practitioner in knowing theintegrated effect of a patient's eye and a test lens placed in front ofthe eye includes means for sensing a wavefront of light returning fromthe eye through the lens. Means are coupled to the wavefront sensingmeans for generating an indication of the integrated effect of the eyeand the test lens.

In another aspect, a device for generating an indication of the qualityof vision of a patient viewing a target includes a light beam generatordirecting light into the eye of the patient, and a wavefront sensingdevice detecting the wavefront in light returned from the eye of thepatient while the patient is looking at the target. A computing devicereceives input from the wavefront sensing device that is representativeof the wavefront. The computing device outputs a continuous update of atleast one of: a point spread function, and a modular transfer function,while the patient is looking at the target. A display device displays atleast one of: a simulated image of the target at the patient's retina, aquality of vision indicator indicating the quality of vision, and agraph indicating a contrast function of the patient, based at least inpart on at least one of the point spread function and the modulartransfer function.

In yet another aspect, a vision quantifying device includes abeamsplitter through which a patient can look at a target. A source oflight emits light into an eye of the patient, which reflects from theeye as a return beam. A processor receives a signal representative of awavefront of the return beam and generates at least one signal inresponse thereto, and a display receives the signal and presents avisual indication of the patient's sight.

Another aspect of the device is to provide automatic refraction process.The patient looks at a target, a test lens is positioned between thetarget and the patient's eye, and in the line of sight of the patient. Alight beam is directed through the test lens and into the patient's eye.Using a portion of that light reflected from the surfaces within the eyea wavefront profile is reconstructed. From the reconstructed wavefrontprofile, A quality vision factor (“QVF”) may be calculated. In order toimprove the accuracy of the measurements of the patient's eye, a numberof measurements of the returning wavefront profile are taken, and thecorresponding QVF values for each of the measurements for thatparticular test lens, is analyzed. The analysis of this data providesfor a determination that the correction with that particular lens isoptimal. If the correction is not optimal, a next test lens is selected,and the process is then repeated the next test lens after it ispositioned by mechanical means in the patient's line of sight. On theother hand, if the correction with that particular lens is optimal, thanthe process ends and resulting in the proper refractive correctionhaving been identified.

The details of the present invention, both as to its structure andoperation, can best be understood in reference to the accompanyingdrawings, in which like reference numerals refer to like parts, and inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the present apparatus, in one intendedenvironment;

FIG. 2 is a perspective view of the apparatus, showing a patient inphantom;

FIG. 3 is a block diagram of the components of one preferred apparatus;

FIG. 4 is a flow chart of the presently preferred logic;

FIGS. 5-9 are exemplary non-limiting diagrams of quality of visiondisplays; and

FIG. 10 is a flow chart showing the automatic refraction method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIGS. 1 and 2, an apparatus of the presentinvention is shown, generally designated 10, and includes a housing 12that can be mounted on a movable stand 14 for positioning the housing 12in front of a patient 15 who might sit in an examination chair 16. Ascan be appreciated in cross-reference to FIGS. 1 and 2, the patient 15can position his or her head against the housing 12. Alternatively, thehousing 12 can be supported on the head of the patient 15 and/or besuspended from a flexible overhanging arm which may be attached to astand, to provide weight balance and to facilitate mounting anddismounting of the head mounted-apparatus. Or, the apparatus of thepresent invention can be co-mounted with a conventional phoropter (notshown), in which case the test lenses of the present invention can beestablished by the lenses of the conventional phoropter.

Now referring to FIG. 3, the patient 15 can look through the housing 12to a target 18, such as but not limited to a Snellen chart. The target18 can be positioned at any appropriate distance from the patient 15,e.g., twenty feet or closer. Since the target 18 can be positioned at adistance that actually is the distance intended, the above-noted patientaccommodation effects related to autorefractors, are reduced oreliminated.

FIG. 3 shows one exemplary implementation of the housing 12. While FIG.3 shows that various components are located inside the housing 12 andvarious other components such as the output display is located outsidethe housing 12, it is to be understood that the principles advancedherein apply to phoropter systems having multiple housings, or a singlehousing.

In the embodiment shown, the patient looks at the target 18 through atransparent window within the housing 12, such as can be established bya primary beamsplitter 20. Interposed in the line of sight of thepatient 15 are one or more movable test, or test lenses 22. By “movable”is meant physically movable by hand or computer-controlled mechanism “M”as indicated as M in FIG. 3, and more fully disclosed below to beselectively interposed within or without the line of sight of thepatient 15, or movable in the sense that a variable focal length lenscan be used, with its optical characteristics being variable inaccordance with principles known in the art, for example those utilizedin various designs of autorefractors. That is, the test lens 22 can be,but not limited to, a single concave convex lens, or a combination ofoptical components, including a cylindrical lens and a prism.

As also shown, a light source such as but not limited to a laser 24generates a light beam 26 that can be directed, in one preferredembodiment, toward a laser beamsplitter 28. The laser beamsplitter 28reflects the light beam 26 toward the primary beamsplitter 20, which inturn reflects the beam through the test lens 22 and onto the eye of thepatient.

The beam 26 is then reflected by the eye of the patient 15, back throughthe lens 22, and is reflected off the primary beamsplitter 20. The beampasses through the laser beamsplitter 28, and a portion of the beam isreflected off a pupil detection beamsplitter 30 toward a pupil lightdetector 32 through one or more focussing lenses 33, for purposes to beshortly disclosed. A portion of the return beam passes through the pupildetection beamsplitter 30 and propagates through an optical relay unit34, which focusses the beam onto a wavefront analyzer optics 36. Thewavefront analyzer optics 36 generates a signal representative of thewavefront of the return beam, and a wavefront detector 38 transforms thesignal into an electrical signal for analysis by a processor 40. In onepreferred embodiment, the processor 40 can be associated with controlelectronics known in the art for undertaking control of one or morecomponents (e.g., the light source 24) of the system 10 as more fullyset forth below. Also, the processor 40 can generate the below-describedvisual indications of the patient's vision as corrected by the test lens22 and can cause the indications to be displayed on a display 42, suchas a video monitor, that can be mounted on the housing 12 or aparttherefrom. Or, the display 42 can be a liquid crystal display that canbe mounted on the housing 12 of the system 10, or a standalone displayunit conveniently located for the examiner's viewing. Suitable displaysmay include, but not be limited to, numerical and/or graphicalrepresentations indicative of the patient's quality of vision, moredetails are provided in the following.

If desired, an illumination light 44, e.g., a ring-shaped fiber optic,can be mounted on the housing 12 and can be connected to the processor40 to control the pupil size of the patient 15. The illumination light44 can be a source of diffused light. The light intensity of theillumination light 44 is controlled by the processor 40 in response tofeedback from the pupil light detector 32, which can comprise a CCDcamera, or reticon detector arrays to monitor the size of the pupil, sothat a predetermined pupil size can be maintained for the patient duringthe measurement. The locations of the pupil detection unit, includingthe components, beamsplitter 30, lens 33, and pupil light detector 32can be in other appropriate locations along the optical path of thereturn light from the eye, including locations inside the optical relayunit 34.

As a further improvement to the accuracy of the refraction measurement,the system also monitors the first Purkinge image, an image formed byreflection at the anterior surface of the cornea of the light beam 26.The position of this image relative to the pupil boundary is anindication of gazing direction of the patient under examination. Unlessthe patient has strabismus in that eye, the relative position of theFirst Perkinge image is a well defined bright spot, and it is typicallyinside the pupil boundary. Therefore, in a preferred but non-limitingembodiment, the pupil detector 32 can also function as a patient gazingmonitor. In this case, the relative position of the First Perkinge imageto the pupil is determine by processing of the image data from the CCDcamera, for example, using data filtering, contrast enhancement, andpupil boundary determination methods known in the art.

All software processing can be done in real time in a matter of afraction of a second. The objective of this analysis is to determinewhether the patient is looking at the target, or momentarily driftingoff. The information is electromagnetically transmitted to the centralcontrol unit 40. If the patient is not looking at the target, the dataset from the wavefront detector unit 38 is rejected, and shall not bedisplayed or accumulated for data analysis.

The following comments are germane to implementation details ofpreferred, non-limiting embodiments. The light source 24 can be a diodelaser that emits light at near infrared wavelengths. Moreover, the lightdetectors 32, 38 can be implemented by CCD arrays or linear reticonarrays. Further, the primary beamsplitter 20 can be coated to transmitvisible light and to reflect infrared light. On the other hand, thelaser beamsplitter 28 can be a polarization dependent reflector, inwhich case the laser light is polarized, and a quarter wave plate (notshown) is disposed in the beam path to the patient 15 such that thereturn beam is rotated ninety degrees (90°) upon double passing thequarter wave plate for facilitating passage thereof through the laserbeamsplitter 28 toward the wavefront analyzer optics 36. Alternatively,the laser beamsplitter 28 can be plate coated for high transmission andlow reflectivity at forty five degrees (45°) incident angle, such thatonly a small portion of the laser light is reflected into the eye, but ahigh percentage of the return light propagates through the laserbeamsplitter 28.

Continuing with the implementation details of a preferred, non-limitingembodiment, the optical relay unit 34 can include two convex lenses F1and F2 that together establish a telescope. The lenses F1, F2 areseparated from each other by a distance equal to the sum of their focallengths, with the focal plane of the first lens F1 being located at thefront surface of the test lens 22, i.e., the surface facing the primarybeamsplitter 20. The focal plane of the second lens F2 is located at theimage plane of the wavefront analyzer optics 36. The purpose of thetelescope structure of the relay unit 34 is to relay the wavefront atthe exit surface of the test lens 22 to the image plane of the wavefrontanalyzer optics 36. Alternative relay optics can be used to achieve thesame purpose.

With respect to the non-limiting details of the wavefront analyzeroptics 36, the optics 36 can include an array of lenslets arranged as ina Shack-Hartmann wavefront sensor, an example of which can be found inpage 37, “Customized Corneal Ablation The Quest for Super Vision” editedby MacRae, et. al. published by Slack Incorporated, 2001, incorporatedherein by reference. Various Shack-Hartmann wavefront sensors andprocessors are available, for example, from commercial vendors such asWavefront Sciences, in Albuquerque, N. Mex., Zeiss/Humphrey Instruments,in Dublin, Calif., or Bausch and Lomb, in Irvine, Calif. Morepreferably, the optics 36 can include ruled reticles such as thosedisclosed in co-pending application U.S. patent application Ser. No.10/014,037, entitled “SYSTEM AND METHOD FOR WAVEFRONT MEASUREMENT”,filed Dec. 10, 2001, incorporated herein by reference, which uses aself-imaging diffraction principle to detect the wavefront in the returnbeam.

Regardless of the type of wavefront analyzer optics 36 used, theprocessor 40 analyzes the profile of the wavefront of the light returnedfrom the patient's eye, and quantifies the wavefront aberrations in tworegimes: low order aberrations, including spherical refractive error,cylinder, and axis, and higher order aberrations, including coma,spherical aberrations and other higher order terms that can be describedby Zernike polynomials. Quantitative data representing the patient'squality of vision are then graphically presented on the display 42.

Now referring to FIG. 4, an exemplary mode of operation of the presentinvention can be seen. The patient 15 views the target 18 through thephoropter system 10, and in particular through the transparent windowthat is established by the primary beamsplitter 20. At block 44 theexaminer initiates the vision test by inserting a selected test lens 22in the line of sight of the patient, or by configuring a variable focallength lens 22 to have a predetermined focal length. Inserting meanseither a manual positioning or positioning using a motorized means. Or,the processor 40 can select a particular lens 22 and cause it to beautomatically moved in the line of sight, in accordance with disclosurebelow.

Proceeding to block 46, the processor 40 determines the point spreadfunction (PSF) that is derived from using, for instance, the terms ofZernicke polynomials, which is in turn derived from the wavefrontpassing through the wavefront analyzer optics 36 and transformed into anelectrical signal by the wavefront detector 38 at the instant when thewavefront data is acquired. The processor 40 Fourier transforms thesignal from the wavefront detector 38 using the following equation:

PSF(x, y)=FT(P(x, y))|²

wherein FT designates a Fourier Transform calculation and P(x, y) is thespatial distribution of the wavefront profile of light with the samephase (phase front) returned at the corneal plane.

Proceeding to block 48, if desired an Optical Transfer Function (OTF)can be calculated from an inverse operation of Fourier Transform asfollows:

OTF(f _(x) , f _(y))=FT ⁻¹(PSF(x, y)),

wherein f_(x), f_(y) are spatial frequencies in x and y directions,respectively, that are orthogonal to each other.

Moreover, a Modular Transfer Function (MTF) can be determined as theamplitude of the OTF:

MTF(f _(x) , f _(y))=|OTF(f _(x) , f _(y))|.

The above functions are used to generate visual indications of thequality of vision that is afforded by the test lens 22 currently beingviewed by the patient 15. For instance, once the PSF is determined atblock 46, the logic can flow to block 50 to determine a convolutionalfunction G as follows:

G(x _(img) , y _(img))=∫∫PSF(x−x _(img) , y−y _(img))f(x _(img) , y_(img))dx dy,

wherein f(x_(img), y_(img)) is the test target 18 (FIG. 3), i.e., anideal image function, x−x_(img) is the difference in the x-dimensionbetween each point in the PSF and the corresponding ideal point in theideal image, and y−y_(img) is the difference in the y-dimension betweeneach point in the PSF and the corresponding ideal point in the idealimage.

The convolutional function G can be used at output state 52 to generatean appropriately blurred image, point by point, of an ideal image asaffected by the imperfection of the patient's eye in combination withthe lens 22. For example, when the target 18 is a Snellen chart, theideal image function can be the letter “E” or a series of other letters,e.g., of various physical sizes as conventionally used in the variouslines in the Snellen chart. FIG. 5 shows one such blurred image at 54,which can be presented on the display 42. Alternatively, the target canbe a picture, and the convoluted image G(x_(img), y_(img)) of thepicture is blurred point by point, according to the PSF, whichrepresents an image of the target formed at the patient's retina.

Accordingly, the letters in the simulated blurred image have the sameblurring as perceived by the patient 15. In this way, the examiner canvisualize the clarity and sharpness of the image as a result of the lens22 as it is perceived by the patient 15.

Alternatively or in addition to the image shown in FIG. 5, the processor40 can generate the displays shown in FIGS. 6-8 as follows. At block 56the wavefront profile, as indicated by the above-mentioned linearcombination of Zernike polynomials, is filtered to eliminate terms withcoefficient below a threshold amplitude. Moving to block 58, apsychometric weighting factor “P” is inserted for each of the remainingZernike terms as shown in the following. This weighting factor “P”represents the effect of the brain to discriminate objects despitecertain types of ocular aberrations. For example, most people candiscern a letter in a Snellen chart with a certain amount of defocuswhile the same amplitude of aberration in coma would not allow the samepatient to discern that letter. To compensate for this, a Quality ofVision Factor (QVF) is determined as follows:

QVF=exp(−(Σ_(n) P _(n) Z _(n) ²))

wherein P_(n) is the psychometric weight factors for the correspondingn^(th) term of the Zernike polynomials, and Z_(n) is the coefficient ofthe n^(th) term of the Zernike polynomials in the PSF.

The psychometric weighting factors “P” can be determined by presenting aparticular aberration to a normative group of people, for example,between one hundred to four hundred people, depending on the accuracylevel desired and the range of the scatter value of each type ofaberration measurement. The patients are presented one at a time withparticular types of aberrations selected from the Zernike polynomials,and then the patients are scored for the extent of success in discerningthe target, for example, by the number of letters correctly read on theSnellen chart, or other standardized vision test chart. Other scoringmethods base on contrast level, standardized letter size, sine or squarewave patterns can also be used as targets.

The presenting means can be an aberration plate on which a selected typeof aberration has been imprinted. For example, the aberration type canbe a coma, or a trefoil, having the refractive index profile asspecified by the corresponding Zernike polynomial.

The relative effect of each type of aberration is tabulated for thegroup and averaged to obtain statistically meaningful weight factors.For most practical purposes, Zernike coefficients for terms higher thenthe sixth order (term number twenty nine or higher) minimally contributeto the overall aberration profile of normal eyes. The method ofproducing various types of aberrations with desired amplitudes accordingto each of the Zernike terms is set forth in co-pending U.S. patentapplication Ser. No. 09/875,447 filed Jun. 4, 2001, incorporated hereinby reference. In the event that no data for the psychometric weightfactors are available, all weighting factors P_(n) can be set to unity.

Once the QVF has been determined, one or more of the displays shown inFIGS. 6-8 can be generated and displayed as indicated in block 60. Forexample, as shown in FIG. 6, a bar chart display can be generated topresent an overall indication of the patient's quality of vision asafforded by the lens 22 under test. As shown, the indicator can be inthe form of a graduated bar 62, the height of which is proportional tothe QVF determined at block 60, with zero indicating poor vision andperfect vision being indicated by a bar extending from the bottom to thetop 64 of the scale. If desired, the display scale can be a log scale,in which case the “best” is indicated by the bar 62 being at zero, andrising logarithmetrically with worse vision using a root-mean-squarefunction of the QVF. Enhancements to the bar 62 such as color-coding canbe used. For instance, the bar 62 can be colored red for poor vision andgreen for good vision, with other colors being used to indicateintermediate qualities of vision. In lieu of the bar chart of FIG. 6,the QVF can be used to generate a pie chart as shown in FIG. 7, with thesize of a pie slice 66 relative to the entire circle being linearly orlogarithmetrically proportional to the QVF.

The system 10 can continuously measure the wavefront profile of thelight beam returned from the patient's eye. Accordingly, in onepreferred, non-limiting embodiment, a sequence of QVF measurements(e.g., twenty) for a single test lens 22 can be made in a second or twoand grouped together.

As described earlier, the measurement accuracy can be improved bymonitoring the gazing direction of the patient, and the computing devicein block 40 can reject the data points acquired when the patient was notlooking at the designated target. Furthermore, the computing device canalso accumulate data and perform calculations for average values andstandard deviation for selected subsets of measurement.

FIG. 8 shows a resulting display. As can be appreciated from theexemplary embodiment shown, five lenses 22 have been tested and severalQVF values obtained over a short period for each. Each group of QVFvalues is plotted as a respective vertical line 68 on a plot of QVFversus lens, with the length of each error bar line 68 representing thestandard deviation of the measurements for that particular lens and thecenter of each line representing the mean QVF value. The prescriptioncan be based not only on a high mean QVF value, as indicated at points70 and 72, but also on a small standard deviation, as indicated by bar74. That is, the lens corresponding to the bar 74 might be selectedbecause its QVF values had a small standard deviation from each otherand it had a high mean QVF value, even if not as high as the point 70.This recognizes that some patients prefer a lens power which may notnecessarily provide the sharpest image but which does result in morecomfort, since a patient does relatively little searching for the“better focus” using lenses that exhibit smaller standard deviations inthe QVF. For example, a patient did not have a vision check for anextended period of time, and the required correction is more than 1.5diopters in cylinder, for example. The patient may feel uncomfortablewith the full correction as afforted by the sharpest image, rather thepatient prefers a smaller amount of correction which representsimprovement in his vision, yet not causing dizziness or head strains.Therefore, the present invention provides objective data based on thesubjective response of the patient to a test lens set 22 presented tothe patient.

As recognized by the present invention, to diagnose a patient'scontrast, the patient can be presented with a series of standardizedpatterns of sine wave gratings of increasing spatial frequencyfrequencies, with the patient offering subjective responses. Theresulting examination report can be a curve that depicts a cutoffcontrast intensity at various spatial frequencies. The present inventioncan provide a quantitative evaluation of a patient's contrast, which canbe generated in addition to or in lieu of those displays disclosedabove. Such a display can be generated at output state 76 in FIG. 4 andis shown in FIG. 9, showing a curve 78 depicting actual patient opticalcontrast function (OCF) and a reference curve 80 depicting adiffraction-limited reference. To determine OCF, the following relationis used:

OCF=MTF×M _(lat.)

wherein MTF is the modulation transfer function determined at block 48and M_(lat) is a mathematical function accounting for the low frequencyfiltering of the neural system, the value of which linearly increaseswith spatial frequencies with a slope of unity in a log—log scale plotand reaching the maximum value of one at and above the spatial frequencyof seven cycles per degree.

Accordingly, the OCF does not include the effect of the brain processingat frequencies higher than seven cycles per degree, but it does providevaluable information about the patient's ability to discern sinegratings of various spatial low frequencies based on a patient's optics.

The above process of measuring and displaying indications of theimprovement in vision afforded by a particular test lens 22 to thepatient 15 can be continued at block 82 until the “best” test lens isfound. This can be done by the examiner manually swapping lenses 22 asin a conventional phoropter, or, as mentioned above, the positioning oftest lenses 22 can be done automatically by the processor 40 controllingthe moving mechanism “M”, which can include a motor and couplingstructure connecting the motor to one or more lenses 22, such that themechanism follows an instruction from the processor 40 to insert theparticular lens in the line of sight of the patient, as requested by theprocessor.

When done by the processor 40, the sequence of test lenses 22 to be usedin an examination may be programmed into the processor 40 in accordancewith examination strategy and routines known in the art. The startinglens can be selected based on the patient's current spectacleprescription or based on the wavefront measurement without any test lens22 in the patient's line of sight. Consequently, in reconstructing thereturn beam wavefront without a test lens 22 being in the beam path, theprocessor 40 essentially models the uncorrected aberrations of thepatient's eye in Zernike terms. Recall that the second order Zerniketerms represent defocus, astigmatism and axis information. Based on thepatient's pupil size and the uncorrected wavefront error amplitudes, theprocessor 40 can determine the equivalent diopter power in sphere andcylinder and its axis, and select the appropriate lens 22 being used tostart the examination. In selecting test lenses 22, the processor 40 canuse the above-disclosed QVF values in lieu of subjective responses fromthe patient, and can then execute the examination strategy as if it isperformed with the subjective response from the patient.

The automatic refraction process is depicted in FIG. 10, and generallydesignated 100. Process 100 begins with a first step 102 wherein thepatient looks at a target. In step 104 a test lens is positioned betweenthe target and the patient's eye, and in the line of sight of thepatient. A light beam is directed through the test lens and into thepatient's eye in step 106. A portion of that light is reflected from thesurfaces within the eye and returns along the line of sight of thepatient.

In step 108, the light returning from the patient's eye is detected.From this detected light, the wavefront profile may be reconstructed, asshown in step 110. From the reconstructed wavefront profile, the qualityvision factor (“QVF”) may be calculated in step 112. In order to improvethe accuracy of the measurements of the patient's eye, “N” number ofmeasurements are performed using the returning light. Thereby, “N”wavefront measurements are taken, thereby yielding N wavefront profilesand corresponding QVF values. These successive measurements are taken byreturning from step 112 to step 108, in which the returning light isagain detected “N” times.

Once “N” measurements have been taken and the QVF for each measurementhas been calculated, the QVF for that particular test lens, is analyzedin step 114. The analysis of this data provides for a determination thatthe correction with that particular lens is optimal. This decision ismade in step 116, and if the correction is not optimal, a next test lensis selected in step 120, and the process returns to step 104 where thenext test lens is positioned in the patient's line of sight. On theother hand, if the correction with that particular lens is optimal, thanthe process ends in step 122 resulting in the proper refractivecorrection having been identified.

In a typical automatic refraction process, a series of lenses in ¼diopters increments are used to determine the patient's opticalcorrection. However, the present invention contemplates using more orless than the typical number of lenses, and the diopter increments canbe in ⅛ instead of ¼, depending upon the magnitude of correctionnecessary. Also, as shown in FIG. 10, a number (“N”) of measurements ofthe returning light are taken in steps 108 through 112 to calculate theVQF for the particular test lens. Typically, “N” will equal for example,10-20 separate measurements being taken to provide an accuratemeasurement of the VQF. However, the present invention contemplatestaking more or less than the typical number of measurements dependingupon the particular wavefront sensor device used, and the magnitude ofcorrection necessary.

The prescription can be determined by a person viewing the display ofFIG. 8, or automatically by the processor 40 based on a high QVF valueand low standard deviation, as follows: The examiner, or the processorwill examinate the curve shown in FIG. 9, which connects the averagevalues of the QVF's for various lens sets presented to the patient. Animprovement may include the step of performing a best fit to the averagevalues, suing a polynomial of up to 4 order, for example. The processorsearches for the maximum value, of the “peak” of the curve. This can beaccomplished by monitoring the peak value of the curve, or slope of thecurve from decreasing lens power, from right to left, in FIG. 8. Whenthe curve reaches its maximum value, the slope changes sign, and themaximum is at the zero slope value. Now, the processor send the peakvalue of the QVF and the corresponding lens power to the display or aprinter.

Additionally, the processor also searches for the minimum value amongthe standard deviation in the data set as shown in FIG. 8. A figuresimilar to FIG. 8 showing standard deviations versus lens power can beuseful (not shown) in determining the minimum value, suing the steps ofa best fit curve, and search for the sign change of the slope asdescribed above for determining the maximum QVF value. Again, thisminimum standard deviation value and the corresponding lens power aresent to the display or a printer for record. For example, on the displayor the printout the processor may indicate that lens power with themaximum QVF value provides for the sharpest image, while the lens powerwith the minimum standard deviation provides for the most comfortableprescription to the patient.

While FIG. 3 illustrates a system 10 wherein the return beam from thelens 22 is detected and analyzed and, hence, the integrated effect onthe wavefront introduced by the eye and lens 22 is measured, it is to beunderstood that as mentioned above the return beam from the eye can alsobe analyzed without passing through the lens 22. In such an embodiment,the effect of the lens 22, which has a known deviation from spherical,can be accounted for by adding or subtracting the lens 22 effect asappropriate from the eye-only wavefront. To facilitate this, a sensor(not shown) can be provided that senses which lens 22 is moved into thepatient's line of sight. The sensor sends a signal representative of thelens (and, hence, of the optical contribution of the lens) to theprocessor 40.

In any case, it may now be appreciated that if desired, the examiner canuse conventional tactics in the steps of selecting test lenses 22 as ifthe whole process were done using a conventional phoropter that requiressubjective responses from the patient. For example, the examiner can use“fogging” in accordance with principles known in the art to form anartificial image before the retina of the patient to cause the patientto relax the above-mentioned accommodative power. However, owing thepresent display capability of the system 10, the examiner can identifythe test lens 22 with which the patient achieves good vision withoutaccommodation, regardless of patient verbal cooperation or ability tojudge and articulate which lens 22 is best. That is, by observing thepresent displays and continuing to decrease the focusing power of thetest lenses being used and moving the image behind the patient's retina,the examiner can determine the range of accommodation of the patient.

Once the best lens 22 has been identified, the examiner may indicatethis decision by pressing a “finish” button (not shown), and a printoutof the examination result can be output using a printer or similardevice (not shown) that is connected to the processor 40. The processor40 may also automatically transmit via modem, internet or otherappropriate means, the prescription to a remote location for lensmanufacturing. A prescription to correct low order aberrations includingsphere, cylinder and axis, can be used for prescribing conventionalophthalmic lenses, or a “supervision” prescription to correct all ordersof aberrations can be used to prescribe improved vision lenses, such asare described in co-pending U.S. patent application Ser. No. 10/044,304,filed Oct. 25, 2001 and incorporated herein by reference.

While the particular APPARATUS AND METHOD FOR DETERMINING OBJECTIVEREFRACTION USING WAVEFRONT SENSING as herein shown and described indetail is fully capable of attaining the above-described objects of theinvention, it is to be understood that it is the presently preferredembodiment of the present invention and is thus representative of thesubject matter which is broadly contemplated by the present invention,that the scope of the present invention fully encompasses otherembodiments which may become obvious to those skilled in the art, andthat the scope of the present invention is accordingly to be limited bynothing other than the appended claims, in which reference to an elementin the singular is not intended to mean “one and only one” unlessexplicitly so stated, but rather “one or more”. All structural andfunctional equivalents to the elements of the above-described preferredembodiment that are known or later come to be known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the present invention, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited as a “step”instead of an “act”.

What is claimed is:
 1. An apparatus for determining the refraction andaberrations of a patient's eye focused on an external physical target,comprising: a light source; optics directing light from said lightsource to the patient's eye; a test lens having an optical power, saidtest lens disposable in an optical path between the patient's eye andsaid external physical target, such that the patient'eye looking at saidexternal physical target receives light from said light source throughthe lens; at least one wavefront measurement device positioned to detectaberrations in light returning from the patient's eye; a housingcontaining said optics and said test lens, said housing having an inputport and an output port, said optical path between the patient's eye andsaid physical target passing through said input port into said housingand through said output port thereby exiting said housing, said targetbeing external to said housing; and processing electronics configured tocompute variation in multiple wavefront measurements performed by saidwavefront measurement device using said test lens having said opticalpower to measure a patient's subjective response to said optical power.2. The apparatus of claim 1, wherein said housing further comprises asubstantially transparent window in said optical path between thepatient's eye and said external physical target through which thepatient's eye views said external physical target, said windowseparating said optical path into a portion inside said housing and aportion of said optical path external to said housing.
 3. The apparatusof claim 1, wherein the light source includes a laser for generating thelight and said laser is within said housing.
 4. The apparatus of claim1, wherein the wavefront measurement device includes at least one lightdetector receiving a wavefront from the light returning from thepatient's eye, and outputting a signal representative of theaberrations.
 5. The apparatus of claim 4, further comprising at leastone visual display configured to receive input from said processingelectronics generated substantially instantaneously by said processingelectronics using the diagnostic signal from the light detector, saidprocessing electronics and said display configured to generate at leastone data representation selected from the group consisting of (1) animage generated by a convolution of the image of the target based on thewavefront returning from the patient's eye and through the test lens;(2) a numerical and/or graphic display representative of theeffectiveness of the test lens; (3) a numerical and/or graphic displayof the contrast function of the patient's vision.
 6. The apparatus ofclaim 5, wherein said processing electronics is configured to providethe visual display with representations selected from the groupconsisting of a bar chart, a pie chart, and a line chart.
 7. Theapparatus of claim 5, wherein the visual display comprises a colordisplay and said data representation is color coded, said processingelectronics being configured to provide input to said color display tocreate said color coded data representation.
 8. The apparatus of claim4, wherein the wavefront measurement device includes electronics thatoutputs a diagnostic signal substantially instantly, and wherein saiddiagnostic signal corresponds to the objective assessment of quality ofvision.
 9. The apparatus of claim 8, wherein said processing electronicsis configured to generate an image representative of the target as seenby the patient's eye.
 10. The apparatus of claims 9, wherein saidprocessing electronics is configured to use said objective assessment ofquality of vision to select a next lens to determine a successiveobjective measurement of quality of vision corresponding to said nextlens.
 11. The apparatus of claim 8, wherein said processing electronicsis configured to use the diagnostic of signal for generating at leastone visual display representative of an effectiveness of the lens incorrecting a patient's vision.
 12. The apparatus of claim 8, whereinsaid processing electronics is configured to compute the standarddeviation of said objective measurement of quality of vision and one ormore successive objective measurements of quality of vision andidentifies an optimal vision correction lens for the patient.
 13. Theapparatus of claim 1, wherein said processing electronics are configuredto compute the standard deviation of multiple wavefront measurementsperformed using said test lens having said optical power to assess apatient's subjective refraction.
 14. An apparatus for determining therefraction of a patient's eye focused on a physical target, saidapparatus comprising: a light source; optics directing light from saidlight source to the patient's eye, said light reflecting from a surfaceof said eye, said reflected light comprising a plurality of wavefronts;a wavefront measurement device positioned along a first optical path tosaid eye to measure the shape of said wavefronts reflected from thepatient's eye; at least one test lens disposable along a second opticalpath between the patient's eye and the physical target; and processingelectronics configured to determine the variation in multiple wavefrontmeasurements that are performed by said wavefront measurement device fora fixed amount of refractive correction using said at least one testlens having said fixed refractive correction to quantify accommodationof the patient's eye, wherein said optics and said at least one testlens are arranged such that when said patient looks at said physicaltarget through said test lens, said light from said light source isdirected through said eye so as to determine said refraction from saidwavefronts returning from said eye.
 15. The apparatus of claim 14,further comprising a beamsplitter for merging said first optical pathfrom said wavefront sensor to said eye and said second optical path fromsaid eye to said physical target such that they overlap in a regionbetween said beam splitter and said eye.
 16. The apparatus of claim 15,wherein said test lens is disposed in said region between said patient'seye and said beamsplitter where said first and second optical pathsoverlap.
 17. The apparatus of claim 14, wherein said test lens ispositioned an optical path length of L from said physical target, saideye being adjusted to view said physical target said distance, L, awayfrom said eye.
 18. The apparatus of claim 17, wherein said distancebetween said eye and said physical target is about 20 feet.
 19. Theapparatus of claim 14, further comprising a housing containing saidoptics, said wavefront measurement device, and said at least one testlens, said housing having an input port and an output port, said secondoptical path between said patient's eye and said physical target passingthrough said input port into said housing and through said output portthereby exiting said housing, said physical target being external tosaid housing, wherein said housing includes a substantially transparentwindow disposed in said second optical path between said patient's eyeand said physical target such said patient's eye can focus on saidphysical target, said window separating said second output path into aportion inside said housing and a portion of said second optical pathexternal to said housing.
 20. The apparatus of claim 19, wherein saidlight source comprises a laser and said laser is within said housing.21. The apparatus of claim 14, wherein said wavefront measurement deviceincludes at least one light detector receiving the light returning fromthe patient's eye and sending a signal to at least one processor, saidat least one processor generating at least one diagnostic output basedon said wavefront measurements.
 22. The apparatus of claim 14, whereinsaid processing electronics is configured to determine the standarddeviation of said multiple wavefront measurements performed by saidwavefront measurement device for said fixed refractive correction toquantify accommodation of said patient's eye.
 23. The apparatus of claim14, wherein said at least one lens comprises a plurality of test lenshaving different amounts of refractive correction, wherein saidprocessing electronics are configured to determine variation in multiplewavefront measurements for each of said plurality of test lens so as toquantify accommodation of the patient's eye for each of said pluralityof test lens.
 24. The apparatus of claim 14, wherein said at least onelens comprises an adjustable lens system having a plurality of settingsthat provide different amounts of refractive correction, wherein saidprocessing electronics are configured to determine variation in multiplewavefront measurements for said different amounts of refractivecorrection provided by said adjustable lens system so as to quantifyaccommodation of the patient's eye for each of said different amounts ofrefractive correction.
 25. The apparatus of claim 1, further comprisinga housing containing said optics and said test lens, said housing havingan input port and an output port, said second optical path between saidpatient's eye and said physical target passing through said input portinto said housing and through said output port thereby exiting saidhousing, said physical target being external to said housing.
 26. Anapparatus for determining the refraction and aberrations of a patient'seye focused on a target, comprising: a light source; optics directinglight from said light source to the patient's eye; a test lens having anoptical power, said test lens disposed in an optical path between thepatient's eye and said target, such that the patient's eye looking atsaid target receives light from said light source through the lens; atleast one wavefront measurement device positioned to detect aberrationsin light returning from the patient's eye; and processing electronicsconfigured to determine variation in multiple wavefront measurementsperformed by said wavefront measurement device using said test lenshaving said optical power to measure a patient's subjective response tosaid optical power.
 27. The apparatus of claim 26, wherein saidprocessing electronics are configured to determine the standarddeviation of multiple wavefront measurements performed using the testlens having said optical power to assess a patient's subjectiverefraction.